Development of novel spectroscopic methods for laser-induced dynamic structural change of protein molecules

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In order to develop methods for the laser-induced dynamic structural change of protein molecules, we performed the experimental studies of pump-dump-fluorescence measurements and the observation of IR irradiation effect. PYP (photoactive protein) was selected as a target sample protein because it showed an optical cycle leading to its structural change by the irradiation of a triggering light pulse. Furthermore, THz spectroscopy for protein crystals and the synthesis and evaluation of model compounds for PYP were also performed.Pump-dump-fluorescence measurementsPYP exhibits an optical reaction which is observed as the optical cycle with structural change induced by triggering light. In order to investigate the initial stage of the reaction, pump-dump-fluorescence spectroscopy was employed and compared to time resolved fluorescence spectroscopy which enabled us to trace the excited state dynamics through spontaneous emission of light. In the dump process, the excited state population i … More s dumped by stimulated emission process and the dump efficiency was expected to be proportional to the spontaneous emission. However, the detailed evaluation including that for the saturation effect of the dump intensity clarified that the enhancement of the dump efficiency in the longer wavelength regions existed. This result suggested the potential for controllability of the dump process by controlling the pump-and dump pulse light wave.Observation of IR irradiation effectIR light pulse irradiation effect on the optical cycle of PYP was examined for the IR wavelength region (3μ to 6μ). The femtoseconds IR pulses which were created by a hand-made optical parametric amplifier were applied while Nanoseconds light pulses generated by optical parametric oscillator were used for triggering. The 6 μ IR light pulses was observed to enhance the optical reaction in PYP. Although coincident irradiation of the triggering pulses and the IR pulses were observed to enhance the effect, in order to obtain clear evidence, experimental improvements are continuing for quantifying the effect.THz spectroscopyWe constructed a reflection-type THz spectroscopic system and applied to observe the low-frequency modes of protein crystals of lysozyme. The THz spectroscopy for a protein crystal was succeeded for the first time. Observed spectral shapes depending on the humidity of the crystal were in accordance with the results obtained by Raman scattering spectroscopy. Less